The present invention relates to a coal gasification combined cycle power generation plant or facility which selectively burns a coal gasification fuel and a liquid fuel so as to generate a power and also relates to a method of operating the same, particularly for suitably preventing a combustion gas from conversely flowing into a fuel passage of a coal gasification fuel when using a liquid fuel and for improving a safety in a combustor section.
In recent years, in a viewpoint of an effective utilization of natural resources, there has been made a study and development of a coal gasification power generation equipment which uses a coal gasification fuel as a heat source in a gas turbine power generation plant, a combined cycle power generation plant or the like.
In the coal gasification power generation equipment, a coal gasification fuel is generated from coal by a coal gasification furnace with the use of an air compressed by a gas turbine compressor or oxygen generated by leading the air to an air separator. The coal gasification fuel thus generated is supplied to a gas turbine combustor so as to be burned, and then, by the generated combustion gas, a gas turbine is driven to generate a power.
However, the coal gasification fuel has a worse combustibility as compared with a liquid fuel or a natural gas fuel and has a small calorific value. Further, in the case where a combustion gas temperature in the combustor becomes low, a lot of carbon monoxide is discharged, thus providing a problem in operational characteristics during a low load operation. Therefore, it is desirable to employ a combined cycle facility for compensating the defect of coal gasification fuel by burning other fuels during a starting operation or a low load operation. In such viewpoint, a liquid fuel has been employed as other fuel used in the combined cycle plant.
As described above, the coal gasification combined cycle equipment includes a combustor which can selectively burn a coal gasification fuel gasified coal and a liquid fuel atomized by an atomization air and is constructed in a manner that a combustion gas generated by the combustor is supplied to a gas turbine so that a generator is driven by a power of the gas turbine.
For example, first, the liquid fuel is supplied to the combustor to be burned, and thereby, the gas turbine starts up. When the gas turbine starts up a generation of coal gasification fuel is simultaneously started in a coal gasification furnace. In an operation of the coal gasification furnace during the start-up, an compressed air from an auxiliary compressor or oxygen separated from the compressed air by an air separator is used. After the start-up, an air compressed by a gas turbine compressor or oxygen separated from the compressed air by the air separator is used.
In an operation stage until about one fourth (1/4) load of the gas turbine from the start-up operation, an incomplete coal gasification fuel having a low calorific value is merely generated in the coal gasification furnace. Such a coal gasification fuel is not applicable to a gas turbine operation, and for this reason, the fuel as described above has been conventionally supplied to the combustor.
With a rise of load after that stage, in the coal gasification furnace, a complete coal gasification fuel combustible in the combustor is generated. In this stage, a a combustion operation of using the liquid fuel is changed over to a combustion operation of using the coal gasification fuel, and then, only coal gasification fuel operation is carried out up to a gas turbine rating point.
As described above, the coal gasification fuel has a small calorific value as compared with a liquid fuel or a natural gas. Thus, in the case where a combustion gas temperature in the combustor becomes low, a lot of carbon monoxide is discharged, and therefore, there is a problem in operational characteristics during a low load operation. For this reason, in the case where the gas turbine is in a load dump state or when the gas turbine is stopped, the operation change-over is again made from the operation of using the coal gasification fuel to the operation of using only the liquid fuel.
FIG. 10 is a view schematically showing an entire structure of a combustor included in the aforesaid coal gasification combined cycle power generation plant, and FIG. 11 is an enlarge sectional view showing a fuel nozzle section of the combustor.
As shown in FIG. 10, a combustor 1 is constructed in a manner that a combustor liner 4 used as an inner cylindrical casing is inserted into an outer cylindrical casing 2 with a combustion air passage 3 defined therebetween, a fuel nozzle 5 is provided on an end portion on an upstream side of the combustor liner 4, and a transition piece 6 is connected to a downstream side of the combustor liner 4. An inner circumferential portion of the outer cylindrical casing 2 is provided with a flow sleeve 7 which covers the combustion air passage 3 and functions as an air guide.
The fuel nozzle 5 has a multiple cylindrical structure fixed to a head plate 8 provided on the end portion of the outer cylindrical casing 2. Further, the fuel nozzle 5 is provided, at its outer end positioned on the outside thereof, with a liquid fuel supply port 9 for supplying a liquid fuel, an atomization air supply port 10 for supplying an atomization air for atomizing the liquid fuel, and a coal gasification fuel supply port 11 for supplying a coal gasification fuel.
As shown in FIG. 11, the fuel nozzle 5 is formed with a liquid fuel passage 12 for passing the liquid fuel at the center portion on the internal side thereof, an atomization air passage 13 for passing an atomization air of the liquid fuel at the outer side of the liquid fuel passage 12, and further, a coal gasification fuel passage 14 for passing the coal gasification fuel at the outer side of the atomization air passage 13. These passages 12, 13 and 14 are arranged side-by-side in a manner of being partitioned by cylindrical walls 15 and 16 and communicate with the liquid fuel supply port 9, the atomization air supply port 10 and the coal gasification fuel supply port 11, respectively.
Moreover, an inner end portion of the fuel nozzle 5 facing the inside of the combustor liner 4 is provided with a liquid fuel injection port 17 for injecting a liquid fuel "a" from the liquid fuel passage 12, an atomization air injection port 18 which injects an atomization air "b" around the liquid fuel injection port 17 from the atomization air passage 13 so that the liquid fuel "a" becomes an atomized state, and a coal gasification fuel injection port 20 having a swirler 19 which injects a coal gasification fuel "c" from the coal gasification fuel passage 14 in a rotating state.
During the gas turbine operation, the coal gasification fuel "c" or the liquid fuel "a" in an air atomized state is selectively injected into the combustor 5 from the fuel nozzle 5 by a known means, and a combustion air "d" is supplied into the combustor liner 4 from a gas turbine compressor (not shown) via the combustion air passage 3 to thereby start the combustion. Then, a combustion gas 21 thus generated is supplied to a gas turbine (not shown) via the transition piece 6.
Meanwhile, as described above, conventionally, when the gas turbine is in the stage of start-up, stop or during a load dump, a combustion operation using only the liquid fuel "a" is carried out, and at this time, the supply of the coal gasification fuel "c" is stopped. For this reason, an internal pressure of the coal gasification fuel passage 14 for supplying the coal gasification fuel "c" becomes lower than that of the combustor liner 4 in which the combustion gas 21 generated by the combustion of the liquid fuel "a" is filled. Thus, as shown by an arrow "e" in FIG. 11, by the differential pressure, there happens a phenomenon such that the combustion gas 21 conversely flows into the coal gasification fuel passage 14 from the combustor liner 4 side.
Even in the case where no differential pressure is caused, by a mere change in a kinetic (dynamic) pressure of the combustion gas 21, a pressure change of the combustor 1 or the like, there may be the case where the combustion gas 21 conversely flows into the coal gasification passage 14.
The conversely flowing phenomenon of the combustion gas 21 as described above is a factor of damaging the fuel nozzle 5, hinders the gas turbine operation, and further, makes short the life of combustor. For this reason, various problems are caused in an operation, economics or the like.